1. Field of Invention
This invention relates to recombinant proteins, genes, and gene probes and more specifically to such proteins and probes derived from an enterically transmitted nonA/nonB hepatitis viral agent, to diagnostic methods and vaccine applications which employ the proteins and probes, and to gene segments that encode specific epitopes (and proteins artificially produced to contain those epitopes) that are particularly useful in diagnosis and prophylaxis.
2. Background
Enterically transmitted non-A/non-B hepatitis viral agent (ET-NANB; also referred to herein as HEV) is the reported cause of hepatitis in several epidemics and sporadic cases in Asia, Africa, Europe, Mexico, and the Indian subcontinent. Infection is usually by water contaminated with feces, although the virus may also spread by close physical contact. The virus does not seem to cause chronic infection. The viral etiology in ET-NANB has been demonstrated by infection of volunteers with pooled fecal isolates; immune electron microscopy (IEM) studies have shown virus particles with 27-34 nm diameters in stools from infected individuals. The virus particles reacted with antibodies in serum from infected individuals from geographically distinct regions, suggesting that a single viral agent or class is responsible for the majority of ET-NANB hepatitis seen worldwide. No antibody reaction was seen in serum from individuals infected with parenterally transmitted NANB virus (also known as hepatitis C virus or HCV), indicating a different specificity between the two NANB types.
In addition to serological differences, the two types of NANB infection show distinct clinical differences. ET-NANB is characteristically an acute infection, often associated with fever and arthralgia, and with portal inflammation and associated bile stasis in liver biopsy specimens (Arankalle). Symptoms are usually resolved within six weeks. Parenterally transmitted NANB, by contrast, produces a chronic infection in about 50% of the cases. Fever and arthralgia are rarely seen, and inflammation has a predominantly parenchymal distribution (Khuroo, 1980). The course of ET-NANBH is generally uneventful in healthy individuals, and the vast majority of those infected recover without the chronic sequelae seen with HCV. One peculiar epidemiologic feature of this disease, however, is the markedly high mortality observed in pregnant women; this is reported in numerous studies to be on the order of 10-20%. This finding has been seen in a number of epidemiologic studies but at present remains unexplained. Whether this reflects viral pathogenicity, the lethal consequence of the interaction of virus and immune suppressed (pregnant) host, or a reflection of the debilitated prenatal health of a susceptible malnourished population remains to be clarified.
The two viral agents can also be distinguished on the basis of primate host susceptibility. ET-NANB, but not the parenterally transmitted agent, can be transmitted to cynomolgus monkeys. The parenterally transmitted agent is more readily transmitted to chimpanzees than is ET-NANB (Bradley, 1987).
There have been major efforts worldwide to identify and clone viral genomic sequences associated with ET-NANB hepatitis. One goal of this effort, requiring virus-specific genomic sequences, is to identify and characterize the nature of the virus and its protein products. Another goal is to produce recombinant viral proteins which can be used in antibody-based diagnostic procedures and for a vaccine. Despite these efforts, viral sequences associated with ET-NANB hepatitis have not been successfully identified or cloned heretofore, nor have any virus-specific proteins been identified or produced.
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Novel compositions, as well as methods of preparation and use of the compositions are provided, where the compositions comprise viral proteins and fragments thereof derived from the viral agent for ET-NANB. A number of specific fragments of viral proteins (and the corresponding genetic sequences) that are particularly useful in diagnosis and vaccine production are also disclosed. Methods for preparation of ET-NANB viral proteins include isolating ET-NANB genomic sequences which are then cloned and expressed in a host cell. The resultant recombinant viral proteins find use as diagnostic agents and as vaccines. The genomic sequences and fragments thereof find use in preparing ET-NANB viral proteins and as probes for virus detection.